- Damage them physically
- Downgrade below the factory provided version
- Wipe the NAND
- Pull the battery during update (semi-brick)
- Mess with the NAND
- Use a corrupted MSPD (pseudo-brick)

- Use it as an actual brick

I'll let others fill the gaps.

EDIT: A semi-brick is recoverable. A pseudo-brick is not actually a brick at all, just a black screen as a result of the system not knowing what to do if it can't read the memory card. I posted about it years back when I encountered it for the first time.